The book is arranged with each chapter exploring a separate tactical building block of Domain-Driven Design. It also includes an introduction to Domain-Driven Design, information on how to integrate different Bounded Contexts or applications, and an appendix.
Summary of Chapters
Chapter 1: Getting Started with Domain-Driven Design
What is Domain-Driven Design about? What role does it play in complex systems? Is it worth learning about and exploring? What are the main concepts a developer needs to know when jumping into it?
Chapter 2: Architectural Styles
Bounded Contexts can be implemented in different ways and using different approaches. However, two styles are getting more popular, and they are Hexagonal Architecture and CQRS + ES. In this chapter, we'll see these two main Architectural Styles, understand what their main strengths are, and discover when to use them.
Chapter 3: Value Objects
Value Objects are the basic pieces for rich modeling. We'll learn what their properties are and what makes them so important. We'll figure out how to persist them using Doctrine and custom ORMs. We'll show how to properly validate and unit test them. And finally, we'll see what a test case of testing immutability looks like.
Chapter 4: Entities
Entities are Domain-Driven Design building blocks that are uniquely identified and mutable. We'll see how to create and validate them and how to properly map them using a custom ORM and Doctrine. We'll also assess whether or not annotations are the best mapping approach for Entities and look at the different strategies for generating an Identity.
Chapter 5: Domain Services
In this chapter, you'll learn about what a Domain Service is and when to use it. We'll review what Anemic Domain Models and Rich Domain Models are. Lastly, we'll deal with Infrastructure issues when writing Domain Services.
Chapter 6: Domain-Events
Domain Events are a great Inversion of Control (IoC) mechanism. In Domain-Driven Design, they're important for communicating different Bounded Contexts asynchronously, improving your Application performance using eventual consistency, and decoupling your Application from its Infrastructure.
Chapter 7: Modules
With so many tactical building blocks, it's a bit difficult to know where to place them in code, especially if you're dealing with a framework like Symfony. We'll review how PHP namespaces can be used for implementing Modules. We'll also discover different hierarchies of folders for organizing Domain Model code, Application Code, and Infrastructure Code.
Chapter 8: Aggregates
Aggregates are probably the most difficult part of tactical Domain-Driven Design. We'll look at the key concepts when dealing with them and discover how to design them. We'll also propose a practical scenario where two Aggregates become one when adding a business rule, and we'll demonstrate how the rest of the objects must be refactored.
Chapter 9: Factories
Factory Methods and objects help us keep business invariants, which is why they're so important in Domain-Driven Design. Here, we'll also explore the relationship between Factories and Aggregates.
Chapter 10: Repositories
Repositories are key for retrieving and adding Entities and Aggregates to collections. We'll review the different types of Repositories and learn how to implement them using Doctrine, custom ORMs, and Redis.
Chapter 11: Application
An Application is the thin layer that connects outside clients to your Domain. In this chapter, we'll show you how to write your Application Services so that they're easy to test and keep thin. We'll also review how to prepare request objects, define dependencies, and return results.
Chapter 12: Integrating Bounded Contexts
We'll explore the different tactical approaches to communicate Bounded Contexts and see real implementations. REST is our suggestion for synchronous communication, and messaging with RabbitMQ is our suggestion for asynchronous communication.
Appendix: Hexagonal Architecture with PHP
Here is where you'll find the original article written by Carlos and published by php[architect] in June 2014.
